Abstract During the ontogenetic development of crustaceans, the relative growth of some structures may change, especially during the transition from juvenile to adult. This study describes the relative growth of body structures of Macrobrachium iheringi, and provides information on its population dynamics, such as structure, fecundity, and morphological sexual maturity. The sampling of M. iheringi was carried out in “Ribeirão da Hortelã”, in Botucatu (SP, Brazil). The length of the carapace (CL), abdomen (AL), and ischium (IL), merus (ML), carpus (CrL), propodus (PpL), and dactyl (DcL) of the second right pereopod were measured. In addition, the width of the second abdominal pleura (PW) and propodus height (PpH) were included in analyses. The relationships that best demonstrated the changes in the allometric coefficient were CL vs PpL in males and females. The CL, in which males and females reach morphological sexual maturity, was estimated as 13.3 mm and 11.1 mm, respectively. The sex-ratio differed from the expected 1:1 and was skewed towards females. Precipitation and temperature influenced the abundance of different demographic classes. Macrobrachium iheringi has few but large eggs, which is expected since this species has an abbreviated larval development. Based on these results, we conclude that the propodus are good indicators of the size at onset of morphological sexual maturity. In addition, important information was obtained on the biology of M. iheringi, including its life cycle pattern, reproduction and influence of abiotic factors.

ABSTRACT We analyzed the spatio-temporal variations of the abundance, distribution and the population structure of Hexapanopeus paulensis Rathbun, 1930 from the southeastern Brazilian coast. Monthly samples were taken from January 1998 to December 1999 at Ubatumirim, Ubatuba and Mar Virado bays. A total of 1084 individuals were obtained, 76 specimens at Mar Virado, 322 at Ubatuba and 686 at Ubatumirim. It was possible to verify an association between the abundance of H. paulensis and bottom temperature (positive correlation), grain size of sediment and organic matter content (both negatively). This explains the higher number of individuals in the stations nearest to the continent (with higher temperature values and heterogeneous substrate). Juveniles were recorded throughout the study period, constituting 39.5% of the sampled population, which highlights the importance of the region (especially Ubatumirim Bay, due the highest abundance) for the establishment of the species. Only females occupied the largest size classes, which could mean differential mortality between the sexes or growth rate. Nevertheless, further studies should be accomplished to a better comprehension of such difference.

Abstract This study describes the weight vs. carapace length relationship and provides the total and monthly condition factor values for populations of Macrobrachium jelskii (Miers, 1977) and M. brasiliense (Heller, 1868) occurring in southeastern Brazil. The biological characteristics were compared and related to the climatic environmental factors between the two areas. Our investigation sampled M. jelskii from the Barra Mansa Dam, Mendonça, SP, a semilotic environment with greater resilience than the Talhadinho Stream, Talhado, SP, a lotic environment where specimens of M. brasiliense were captured. Individuals were classified according to sex and measured at the carapace length (CL) and weighed (WE). The relationship WE/CL was analyzed by dispersion diagrams of the empirical points, which were set to the power function (WE = a.CL b ). Values of the mean condition factor were compared monthly. In total, 1493 individuals of M. jelskii and 843 individuals of M. brasiliense were captured. Analyses of the constant allometry revealed that both sexes of M. jelskii, as well as females of M. brasiliense grow proportionately more in size than weight. The results concerning the morphometric aspects studied in both species suggest an association with the reproductive processes.

In this paper, we describe and illustrate the morphology of the first larval stage of the prawn Macrobrachium brasiliense. Two ovigerous females were obtained in a stream environment, which belongs to Paraná River Basin, Southeastern of Brazil, and were maintained in laboratory until the time of hatching. The newly-hatched larva bears very advance morphological features, with benthic habits. They had sessile eyes and all appendages, except for the uropods; however, most of the appendages were not fully formed. The description given here is compared with the first larval stage of Macrobrachium species with abbreviated larval development from other localities.

Some individuals of the species Arenaeus cribrarius (Lamarck, 1818) bear a characteristic pink abdomen, which is notably different from the usual white coloration. The incidence of this chromatic alteration was determined for a single population and its relation with other individual variables were examined. The individuals were monthly collected from May, 1991 to April, 1993, in Ubatuba, São Paulo, with the aid of a shrimp fishery boat provided with double-rig trawling nets. All specimens were sexed, measured (CW = carapace width), distributed in 10-mm size classes and classified according to growth phase (juvenile and adult), molting condition and development stage of gonads. The occurrence of pink-colored morphs was also recorded. From a total of 2,096 collected individuals, only 60 females (nine of those ovigerous) presented a pink-colored abdomen, which represents 2.9% of the whole sample and 5.2% of the females. Almost all of them were intermolt individuals (96.6%) and 63.3% showed mature gonads. According to published data, size at the onset of functional maturity in A. cribrarius females is around 60 mm CW, from which the incidence of pink morphs and ovigerous crabs were recorded. The obtained results suggest that such a chromatic alteration is associated to sexual maturity in these females. This characteristic may enhance the attraction potential for mating, shortly after the puberty molt.